Peripheral Tfh (CXCR5+ CD45RA+ CD27+) cells in HIV+ subjects, particularly in those subjects that do not respond to influenza vaccination, have been found to have elevated expression of inhibitory PD1 and decreased expression of ICOS (a B cell co-stimulator), as well as demonstrating reduced ability to stimulate IgG production when co-cultured with B cells [107]. Here, CD27 is linked to influenza.